Compressor and sliding member thereof

ABSTRACT

Swash plate connected to the driving shaft through lag plate and hinge structure, and slidably connected to edge of each piston through a pair of shoes in front and rear. The rotational motion of the swash plate accompanied by the rotational motion of driving shaft is converted to the reciprocating motion of the piston through shoes. PEEK coating is formed on the swash plate and the shoes that function as sliding members in the invention, at least on the sliding surface. Solid lubricant may be contained in the PEEK coating. Polytetrafluoroethylene (PTFE) is used for example as the solid lubricant.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to improvements in the lubrication of sliding members in a compressor.

[0002] Members that slide against each other during the operation of the compressor need to be lubricated by oil in order to prevent abrasion. The lubrication is usually performed by carrying misted oil onto each sliding member. In other words, lubricating oil held inside a compressor is misted by a gas (refrigerant gas such as chlorofluorocarbon), which is circulated along with the operation of the compressor. The misted oil is transported inside the compressor and adheres onto each member, thereby ensuring good lubrication. However, when restarting the compressor after being stopped for a long period, the lubricating oil that adhered to the sliding members might have been washed away by the refrigerant gas.

[0003] Further, in a swash plate type compressor, a piston is connected to a swash plate through a shoe, and reciprocates in a cylinder bore along with the rotation or the shaking of the swash plate. At the beginning of the operation, the swash plate and the shoe slide against each other before lubricating oil reaches the surfaces on which the swash plate and the shoe slide. The swash plate and the shoe can barely be lubricated by thin lubricating oil residing on their surface from the last operation. However, when gas refrigerant reaches the surfaces of the sliding members and washes away the resided lubricating oil before new lubricating oil reaches those surfaces, the swash plate and the shoe slide under dry sliding condition without any lubricant.

[0004] Accordingly, the supply of the lubricating oil toward the sliding members is insufficient in the period (approximately 1 minute) from the starting of the compressor until misting of the oil proceeds by return of the refrigerant gas to the compressor, in spite of the compressor being operated. Therefore, conventional methods have been proposed to ensure lubrication of the sliding members even during this period.

[0005] As an example of the art for improving the sliding property of sliding members such as swash plate, a method of forming Ni—P plating film on the surface by electroless deposition and a method of forming Al sprayed film on the surface of a swash plate made of iron, have been proposed. In addition, Japanese Patent Application Laid-Open No. Heisei 11-13638 discloses a method in which a plating layer of tin, copper, etc. is formed on the surface of a swash plate comprising a substrate of iron or aluminum (the surface which slides with a shoe), and a layer comprising polyamide imide (PAI) resin and solid lubricant (molybdenum disulfide, graphite, etc.) is formed on the plating layer.

[0006] Further, Japanese Patent Application Laid-Open No. 2000-96203 discloses a method of coating a composition material of polyether-ether-keton (hereinafter referred to as PEEK) on a surface of a metal substrate. This method includes a step of forming a metal binder layer on the surface of a metal substrate, and a step of depositing PEEK composition material on the metal binder layer through a high velocity oxygen fuel (HVOF) process. Also a PEEK composition material coating, coated on a thrust pad of a thrust bearing is disclosed.

[0007] However, sufficient sliding property was not obtained by the methods of forming Ni—P plating film or an Al sprayed film on a sliding surface of a swash plate. Further, although the method disclosed in Japanese Patent Application Laid-Open No. Heisei 11-13638, in which sliding layer comprises polyamide imide resin and solid lubricant, improved the sliding performance compared to the above described method forming Ni—P plate coating, etc., there is still a room for improvement.

[0008] The use of carbon dioxide as a refrigerant of compressor attracts attention recently. If carbon dioxide is used as a refrigerant, the compressive load that acts on the swash plate through piston is markedly increased, compared to the case where Freon (chlorofluorocarbon) refrigerant is used. Accordingly, the sliding environment is more strict when carbon dioxide is used as the refrigerant, therefore even more improved sliding performance is needed.

[0009] The Inventors compared sliding properties between a member in which PEEK is used as a lubricating film, and a member which has a layer comprising combination of polyimideamide resin and solid lubricant. As a result, it was confirmed that the member in which PEEK is used improved sliding property.

[0010] When forming PEEK coating by spraying, PEEK powder is sufficiently heated and is deposited on a substrate in a melted state. However, in the case where flame is used in spraying, such as the method disclosed in Japanese Patent Application laid-Open No. 2000-96203, heating PEEK to exceedingly high temperature degrades PEEK. Further, in Japanese Patent Application Laid-Open No. 2000-96203, a porous metal binder layer is formed on a metal substrate in advance and then melted PEEK material is deposited into each hole of the metal binder layer by HVOF process, thereby ensuring adhesion of PEEK layer even in the case where some particles remained unmelted on the surface, because these particles melt through the material depositing process. However, manufacturing process of PEEK coating becomes more complicated in this method.

BRIEF SUMMARY OF THE INVENTION

[0011] A method of the invention provides sliding members for a compressor with improved lubrication between the members that contact each other, and the manufacturing method thereof is relatively easy.

[0012] In order to achieve the above object, the present invention provides a sliding member used in an operating mechanism of a compressor, said sliding member having a surface slidably connecting a surface of another member, wherein the sliding member is made of at least one metal and has a polyether-ether-keton coating formed at least on a portion of the surface thereof.

[0013] In a preferred embodiment, the present invention provides a swash plate type compressor, which comprises: a swash plate; a piston which reciprocates in accordance with the rotating motion of the swash plate; a shoe which is disposed between said piston and said swash plate; and a first polyether-ether-keton coating formed on said swash plate for contacting the shoe.

[0014] In another aspect of the invention, the present invention provides a swash plate used in an operating mechanism of a compressor, which comprises: a piston coupled to the swash plate; a shoe interposed between the piston and the swash plate, said shoe having a surface slidably contacting a surface of said swash plate; and a polyether-ether-keton coating formed on at least a portion of the surface of the swash plate.

[0015] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

[0017]FIG. 1 shows a cross-sectional view of a compressor according to one embodiment of the present invention.

[0018]FIG. 2 shows a partially enlarged cross-sectional view showing the relationship between the swash plate and the shoe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] Referring to figures, an embodiment is described below in which the present invention is embodied into a variable displacement swash plate type compressor.

[0020] As shown in FIG. 1, compressor C has a cylinder block 1. A front housing 2 is connected to the front edge of the cylinder block 1. A rear housing 4 is connected to the rear edge of the cylinder block 1 through valve plate 3. Cylinder block 1, valve plate 3 and both housings 2 and 4 are mutually fixed by a plurality of throughbolts (not shown in the figures) to construct a housing of the compressor C. Note that the left hand side of FIG. 1 is the front side of the compressor C.

[0021] Crankcase 5, suction chamber 6, and discharge chamber 7 are defined in the housing. A plurality of cylinder bore 1 a (one of which is shown in the figure) are formed in the cylinder block 1. A single head piston 8 is contained in each cylinder bore 1 a and is reciprocatingly movable. Suction chamber 6 and discharge chamber 7 are communicatively connected to each cylinder bore 1 a through intake valve 3 a and delivery valve 3 b provided on valve plate 3.

[0022] Driving shaft 9 is supported rotatably through bearing with respect to cylinder block 1 and front housing 2, and by penetrating crankcase 5. Swash plate 10 is contained in the crankcase 5. Penetrating hole 10 a is formed in the center portion of the swash plate 10 and the driving shaft 9 is penetrated through the penetrating hole 10 a. Lag plate 11 is fixed to the driving shaft 9 to allow integral rotation in the crankcase 5. Swash plate 10 is connected to the driving shaft 9 through lag plate 11 and hinge structure 12. The swash plate 10 is rotatable in synchronization with the driving shaft 9, and is tiltedly movable by sliding in the direction of the axle.

[0023] A counter-weight portion 10 b is integrally formed with the swash plate 10, in the position opposing to the hinge structure 12 in the radial direction by interposing drive shaft 9. Compression spring 13 is wound between the lag plate 11 and the swash plate 10 on the driving shaft 9. Swash plate 10 is forced by the compression spring 13 in the direction toward the cylinder block 1 (or, in an inclination-decreasing direction). Decrease in inclination of the swash plate 10 is limited by contacting to the circlip 14 fastened on the driving shaft 9, to limit minimum inclination θ_(min) of the swash plate 10. Further, maximum inclination θ_(max) of the swash plate 10 is limited by the contact of the counter-weight portion 10 b of the swash plate 10 to the lag plate 11. Note that inclination refers to the angle formed between the orthotomic surface of the driving shaft 9 and the swash plate 10.

[0024] The circumference of the swash plate 10 is slidably connected to edge of each piston 8 through a pair of shoes 15 a and 15 b in front and rear. The rotational motion of the swash plate 10, accompanied by the rotation of driving shaft 9, is converted into the reciprocating motion of the piston 8 through shoes 15 a and 15 b.

[0025] A known control valve 16 is provided in the rear housing 4 for adjusting the crank pressure Pc. The control valve 16 is provided in the midway of the air charging passage, which is not shown in the figures and which communicates the crankcase 5 and the discharge chamber 7, to control the opening of the air charging passage by electromagnetic force by solenoid. The crank pressure Pc is adjusted by balancing the inlet amount of the refrigerant gas from the discharge chamber 7 towards the crankcase 5 through the control valve 16, and the amount of refrigerant gas moving from the crankcase 5 towards the suction chamber 6 through extraction passage not shown figures, which communicates the crankcase 5 and the suction chamber 6.

[0026] PEEK coating 17 is formed at least on a sliding surface of the swash plate 10 and the shoes 15 a and 15 b that function as sliding members in the invention. PEEK coating 17 is directly formed on the surface where the swash plate 10 and the shoes 15 a and 15 b contact each other. Solid lubricant may be contained in the PEEK coating 17. Polytetrafluoroethylene (PTFE) is used for example as the solid lubricant.

[0027] In order to prevent swinging of the angle of the swash plate during rotation due to noise, for example due to the action received by the swash plate from the piston, a relatively heavy iron containing material (cast iron such as FCD 700, etc., for example) is used as the swash plate 10. On the other hand, similar iron-containing material (such as ball-bearing steel) is used for the shoes 15 a and 15 b by considering their mechanical strength, etc.

[0028] In forming PEEK coating 17 on the swash plate 10, firstly powder PEEK is adhered to the sliding surface of the swash plate 10 (surface to slide with 15 a and 15 b) by electrostatic powder coating. Powder PEEK having average grain diameter of for example between 50 and 100 μm is used in the coating. A uniform powdery coating is formed on the sliding surface by performing electrostatic powder coating at room temperature. Next the swash plate 10 is baked in an electric oven. For example, the temperature is raised in 30 minutes from 350° C. to 400° C., and held at 400° C. for 10 minutes. Powder PEEK melts in this period. The swash plate 10 is then removed from the electric oven and quenched with water. The quenched PEEK coating 17 has smooth surface and firmly adhere to the surface of the swash plate 10 although it is a film in which amorphous state and crystalline state are mixed. Annealing treatment is performed for the purpose of stabilizing the crystalline state, and of removing residual pressure. Annealing treatment is performed for example at 240° C. for 1 hour. Crystallization proceeds by the annealing treatment. In order to contain solid lubricant in the PEEK coating 17, mixture of powder PEEK and solid lubricant is used in electrostatic powder coating.

[0029] In order to compare the sliding performance between the PEEK coating 17 and a film formed through conventional technique, testing is performed with respect to disk made of cast iron having the same size as the swash plate 10, to compare: a) the case where PEEK, or combination of PEEK and PTFE is coated; and b) the case where NiPB is plated. The comparison is made using disks that are ground to have surface roughness Rz<3 μm since it is preferable that the surface of the disks are smooth.

[0030] In the sliding test, in order to measure the time until the swash plate seizes under the dry state (without lubricant), the disks formed with coatings were rotated with peripheral speed at 10.4 m/s, and a disk made of SUJ2 having diameter 10 mm was forced against the coating surface at 1,960 N. The times required until both disks seized and locked were measured. The results are shown in Table 1. TABLE 1 Ingredient of the film Time (second) Example 1 PEEK 120 Example 2 PEEK + PTFE 780 Comparative Example 1 NiPB plating 20 Comparative Example 2 NiP + Sn plating 60 Comparative Example 3 PTFE + PAI coating 40

[0031] Referring to Table 1, it was confirmed that a member formed with PEEK coating of Example 1 required a longer time until seizure, in comparison with Comparative Examples 1 through 3, and was superior as a sliding member of a compressor. Further, it was confirmed that the sliding performance was greatly improved in a member of Example 2, which had PEEK coating containing PTFE, compared to a member having a coating comprising only PEEK.

[0032] The action of the compressor formed as described above is next described.

[0033] When the swash plate 10 is integrally rotated with the driving shaft 9, the rotational motion of the swash plate 10 is converted to the reciprocating motion of each piston 8, through shoes 15 a and 15 b. Each piston 8 is reciprocated with a stroke in accordance with the inclination of the swash plate 10. By continuing this operation, refrigerant gas taken in from the suction chamber 6 is compressed in the cylinder bore 1 a, and the compressed gas is discharged to the discharge chamber 7. The refrigerant supplied from an outside refrigerant circulation, not shown in the figures, to the suction chamber 6 is taken into the cylinder bore 1 a through a suction port (not shown), receives compression action due to the motion of the piston 8, and then is discharged into the discharge chamber 7 through a discharge port (not shown). The refrigerant discharged into the discharge chamber 7 is sent away to the outside refrigerant circulation through a discharge hole (not shown).

[0034] Thereafter, the opening of the control valve 16 is adjusted with respect to the temperature in the car interior, or, the cooling load, and the communicating condition between the discharge chamber 7 and the crankcase 5 is changed. In the state where the temperature is high, or, the cooling load is high, and the pressure in the suction chamber 6 is high, the opening of the control valve 16 is small, the pressure in the crankcase 5 (crank pressure Pc) is reduced and therefore the inclination of the swash plate 10 increases. Accordingly, the stroke of the piston 8 is increased, and the compressor is operated at large discharge.

[0035] In the state where the temperature in the car interior, or, the cooling load is low, and the pressure in the suction chamber 6 is low, the opening of the control valve 16 is large, crank pressure Pc is increased and therefore the inclination of the swash plate 10 decreases. Accordingly, the stroke of the piston 8 is smaller, and the compressor is operated at small discharge.

[0036] In the compressor described above, PEEK coating 17, superior in heat resistance, mechanical strength and chemical resistance, is directly formed on the surfaces where the swash plate 10 and shoes 15 a and 15 b slide each other. Accordingly, as well as the sliding performance and durability are improved, manufacture is simpler because the formation of a metal binder layer between the PEEK coating 17 and the member main body made of metal is not required. Instead of forming the sliding member itself from PEEK, PEEK coating 17 is formed on the sliding surface of a main body made of metal. Therefore, necessary strength is secured even in the sliding surface where great load is imposed, such as swash plate 10, through shoes 15 a and 15 b.

[0037] Further, PTFE is contained as a solid lubricant in the PEEK coating 17. Therefore, the coefficient of friction of the PEEK coating 17 is lower and the sliding performance is improved, compared to a PEEK coating 17 which does not contain solid lubricant.

[0038] Moreover, the reliability and the durability of the compressor is improved, since the lubrication performance and the durability of the swash plate 10, which is placed in an extremely strict sliding environment, is improved.

[0039] In addition, the PEEK coating 17 is formed by electrostatic powder coating. Accordingly, formation of PEEK coating 17 with higher bond strength to the member main body becomes simpler than spraying.

[0040] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

[0041] The improved lubricating surface may also be applied to other sliding members, such as piston 8 and lag plate 11, without limiting the application of the coating to the swash plate 10 and shoes 15 a and 15 b. In the case of piston 8, PEEK coating 17 is formed on the sliding surface with the cylinder block 1 and the front housing 2, or the sliding surface with shoes 15 a and 15 b.

[0042] It is sufficient if PEEK coating 17 is formed at least on the sliding surface of the sliding members, and it is also possible to form PEEK coating 17 in the portions other than sliding surface, in addition to the coating towards the sliding surfaces.

[0043] The method for forming PEEK coating is not limited to electrostatic powder coating. Thermal spraying may also be adopted in forming PEEK coating.

[0044] The solid lubricant is not limited to PTFE, and molybdenum disulfide (MOS₂) and graphite, etc., may be used. Further, instead of containing only one kind of solid lubricant, a plurality of kinds of solid lubricant may be contained.

[0045] The material of the swash plate 10 is not limited to iron-containing metals. Aluminum-containing metals (such as aluminum and aluminum alloy) and stainless steel, etc., may also be used.

[0046] The present invention may also be applied to dual head type and fixed displacement type swash plate type compressors, without limiting to variable displacement swash plate type compressors. It may also be applied to a swash plate type compressor in which the swash plate does not integrally rotate with the driving shaft but swings accompanied by the rotation of the driving shaft

[0047] Moreover, the invention is not limited to a swash plate type compressor, and it may also be applied to other types of compressors, such as scroll-type compressor and vane type compressor, etc.

[0048] Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

1. A sliding member used in an operating mechanism of a compressor, said sliding member having a surface slidably connecting a surface of another member, wherein the sliding member is made of at least one metal and has a polyether-ether-keton coating formed at least on a portion of the surface thereof.
 2. A sliding member according to claim 1, wherein the polyether-ether-keton coating contains a solid lubricant.
 3. A sliding member according to claim 1, wherein the polyether-ether-keton coating is formed by electrostatic powder coating.
 4. A sliding member according to claim 1 wherein the compressor is a swash plate type compressor and the member is a swash plate, wherein a piston is coupled to the swash plate and wherein a shoe is interposed between the piston and swash plate, said shoe slidably contacting the swash plate, and a piston.
 5. A swash plate type compressor comprising: a swash plate; a piston which reciprocates in accordance with the rotating motion of the swash plate; a shoe which is disposed between said piston and said swash plate; and a first polyether-ether-keton coating formed on said swash plate for contacting the shoe.
 6. A swash plate type compressor according to claim 5 wherein a second polyether-ether-keton coating formed is on said shoe for contacting the swash plate.
 7. A swash plate used in an operating mechanism of a compressor, comprising: a piston coupled to the swash plate; a shoe interposed between the piston and the swash plate, said shoe having a surface slidably contacting a surface of said swash plate; and a polyether-ether-keton coating formed on at least a portion of the surface of the swash plate.
 8. A swash plate according to claim 7, wherein the polyether-ether-keton coating contains a solid lubricant.
 9. A swash plate according to claim 7, wherein the polyether-ether-keton coating is formed by electrostatic powder coating. 